Tunable magnetrons



Sept. 10, 1957 c. v. LrrToN ETAL 2,806,178

TUNABLE MAGNETRONS Filed Aug. 2o, 195s lftlnited States Patent O TUNABLE, MAGNETRONS Charles Vincent Litton, Redwood City, and Paul W. Crapuchettes, Palo Alto, Calif., asslgnors to Litton Industries, Inc.

Application August 20, 1953, Serial No. 375,532

7 Claims. (Cl. S15-39.61)

This invention relates to magnetrons and in particular magnetrons of the multi-cavity type. More specifically this invention is an improvement over the magnetron disclosed in the U. S. patent entitled Adjustable Magnetron, No. 2,512,901, filed November l, 1945, and issued June 27, 1950.

The above-identified patent discloses a magnetron construction tunable by an L-C ring mounted on a plurality of guide rods and having internally mounted pole pieces. Although the tuning range afforded by the LeC tuning ring is generally satisfactory, means providing still greater tuning ranges are continuously being sought.

Accordingly, it is an object of this invention to provide a magnetron of the mechanically tunable type, having means providing greater tuning and greater efficiency than magnetrons heretofore known.

It is a feature of our invention to provide these improvements without materially changing the size or shape of the magnetron body.

In accordance with a feature of our invention there is provided a tunable magnetron comprising a supporting body and a plurality of cavity resonators for determining substantially a mean frequency to which the magnetron is tuned. Magnetic pole pieces are mounted inside the supporting body and positioned on opposite sides of the resonators. L-C rings are mounted to move unitarily and have tuning portions positioned to enter into or egress from the resonators; the movement of the L-C rings tunes the magnetron over a given range. The present invention provides means for greatly increasing the tuning range and is characterized by providing a movable pole piece positioned on one side of the resonator to provide a variable magnetic flux path between itself and one of the mounted pole pieces.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein the figure is a cross-seetiona1 view of a magnetron; the section being taken through what is essentially the axis of symmetry and showing the tuning element mounted on its guiding structure and the mechanism for adjusting same to the desired position.

Since the general construction of the magnetron is not part of our invention, but is describedin the aforementioned patent, it will be described here only insofar as is necessary for an understanding of the invention.

Referring to the figure, the reference character 1 represents the body of the magnetron to which other parts are brazed or otherwise suitably fastened to form a structure capable of being evacuated. On opposite sides of the body there are brazed to the body 1, cylindrical sections 2 and 3 respectively.

In the cylindrical extension 3 there is mounted a cathode support assembly; the details of this assembly may be found in the U. S. patent, entitled Cathode Support,

ICC

No. 2,474,263, filed November 1, 1945, and issued June 28, 1949. The cathode comprises two filament windings preferably of thoriated tungsten, so mounted and energized as to constitute a bilar filament. One pair of ends of the filament are connected to the power supply over the power supply leads to the terminals 4, 5 and 6 respectively; the terminals being screwed onto threaded rings 7, 8 and 9 respectively. The other pair of ends of each filament are connected to a member 10 which in turn is brazed to a rod 11. The cathode support as described above is suitably rigid for most applications, however, if greater rigidity and freedom from possible vibration is required the rod 11 may be extended and inserted into a bearing in a support ring 12. The support ring also properly centers the cathode and is securely fastened by means of an insulating support 13 positioned within a pole piece 14 as shown.

The pole piece 14 is firmly held in position by staking it to the cylinder 2. A pole piece 15, positioned on the opposite side of a plurality of cavity resonators is divided into two parts 16 and 17. The cavity resonators are defined by a plurality of vanes 15a in a well known manner. Between these parts is positioned a guide ring 18 having a plurality of guide holes therein. Pole piece 1S is held in position within the extension 3 by a support cup 19 as shown. The guide ring 1S is free to expand under the heat of operation of the magnetron. This prevents any binding action which might otherwise occur.

In order to change the resonant frequency of the magnetron two means are provided, one, an L-ring 21, the other, a C-ring 20. The L-C tuning means are explained in the aforementioned patents, and therefore a detailed explanation of these rings will not be made here. Broadly, however, the L-ring comprises a plurality of metal or conducting segments of an annulus. The conducting elements are of a size such that they may freely enter and egress the cavities in the region of the magnetic flux concentration. As the elements enter this region the effective inductance of the cavities is decreased and the cavities become resonant at a higher frequency. The C-ring also comprises a plurality of conducting elements formed in a manner similar to that of the L-ring. The dimensions and size of these elments, however, are auch that they may freely enter or egress the cavities in the region of maximum electric flux concentration. As the elements of the C--ring enter this region the effective capacitance of the cavities is increased and the cavities become resonant fat a lower frequency. The L-ring and the C-ring are mounted on a plurality of metal guide rods 22, 23 and positioned, in general, on opposite sides of the resonant cavities in a manner such that as one ring enters the cavity the other ring emerges therefrom. This provides a better form of variation with respect to the rectilinear motion of the ring and also permits tuning over a considerable frequency range with a small motion. On one side the rods are journaled in the guide holes of the guide ring 1S and fastened to the C-ring 2). Gn the other side the rods are fastened to the L-ring 21.

Oscillatory energy from the cavity of the magnetron is extracted for useful (work by coupling a wave guide 24 to one of the cavities through impedance transformer 25. The impedance transformer and the method of extracting energy from the magnetron is explained in detail in the above-mentioned patents and, therefore, will not be described here.

The extension or housing 2 encloses an assembly 26 for adjusting the frequency to which the magnetron may be tuned. Since the adjusting mechanism does not constitute a part of my invention it will be only broadly described herein. A platform 27 is brazed to a Sylphon the latter being brazed to the housing 2 along the circumference 30 thereof. A rod 31 is brazed to the platform 27 and extends through the bellows and the bearing holder. A hardened and ground sleeve 32 is held in position over the rod by a tongue nut 33 and a loclg nut 34. The bearing 35 is positioned over the sleeve 32 and is clamped against the bottom ofthe bearing holder 29 by an inner ball race. The thrustv bearing ballretainer with balls 37 are held aginst the race 36 by a boltl 38. Relative rotation between the member 39 vincluding the bolt 38 and the sleeve 32 determines .the extent of longitudinal motion of the platform 27. A control knob 46 is fastened to the member 39 for turning the latter.

The above described magnetron is tuned over a given range by moving the L-C rings longitudinally into and out of the resonant cavities. In accordance with the present invention the tuning range is greatly increased by the addition of a movable pole piece element 40. The movable pole piece is enclosed in a copper unit 41; the copper unit being brazed or soldered at one end 42 to the platform 27 of the tuning mechanism, and at the other end to a shouler 43 of the C-ring tuner 20. The movable pole piece 40 is trapped in position by the annular shoulder 44 formed in the copper housing unit 41 and -by the projection 43 formed on the C-ring. A plurality of tungsten wires 45 firmly secured in the fixed pole piece 14 are provided to serve as a bearing for the copper housing 41 as it is moved longitudinally during the tuning of the magnetron. The magnetic flux path traverses a gap between the pole piece 14 and the movable pole piece 40. Therefore, the inductance is varied as the pole piece is moved. Thus, tuning is effected by rotating the control knob 46 which moves longitudinally the pole piece 49. Since the pole piece is attached at one end to the C-ring 2G, and the L-C ring ybeing in eliect a single mechanical member, the movement of the pole piece causes the L-C ring to move unitarily therewith.

Strains, which are usually caused by the unequal expansion of dierent metals which are soldered or brazed together7 are completely avoided because the copper housing 41 is soldered at one end to the copper platform 27 and at the other end to the copper C-ring 20.

The efliciency of the magnetron is greatly improved because the copper housing 41 rapidly conducts the heat from the pole piece to a locality Where the heat is quickly dissipated by water cooling. Consequent mode jumping which sometimes occurs by reason of the pole piece becoming overheated is prevented.

While we have described above the principles of our invention in connection with specific apparatus, it is to'be clearly understood that this description is made only by way of example and not as a limitation of the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

l. A tunable magnetron comprising a supporting body, a plurality of cavity resonators for determining substantially a mean frequency to which the magnetron may be tuned, magnetic pole pieces fixedly mounted inside said supporting body and positioned on opposite sides of said resonators, an L-ring and a C-ring mounted to move unitarily and having tuning portions postioned to enter into or egress from said resonators, means moving said L and C rings for tuning said magnetron over a given range, and means for greatly increasing said tuning range characterized by a movable magnetic pole piece positioned on one side of said resonator and movable intermediate said 4 resonator and the associated fixed pole piece to provide a-variable magnetic Aflux Vpath between itself and one of said mounted pole pieces.

2. The magnetron according to claim l, and further comprising a heat conductive envelope portion, a copper housing surrounding said movable magnetic pole piece and in heat transfer relation to said envelope portion, whereby the heatl developed in the pole piece is rapidly conducted therefrom.

3. The magnetron according to claim 1, and further comprising means f or fastening one end of said movable pole piece to said C-ring, whereby the movement of said pole piece causes the L-C ring to move unitarily therewith.

4. A tunable magnetron comprising a supporting body, a copper envelope portion, a plurality of cavity resonators for determining substantially a mean frequency to which the magnetron may be tuned, magnetic pole pieces mounted inside said supporting body and positioned on opposite sides of said resonators, and LUring and a C-ring mounted to move unitarily and having tuning portions positioned to enter into or egress from said resonators, means moving said L-C rings for tuning'said magnetron over a given range, and means for greatly increasing said tuning range comprising a movable pole piece fastened at one end to said L-C-rings, said -pole piece providing a variable flux path between itself and one of said mounted pole pieces, and a copper housing enclosing said movable pole piece and contacting said envelope portion for rapidly conducting the heat therefrom.

5. A tunable magnetron comprising a supporting body, an external envelope portion, a plurality of vanes mounted inside said ybody integral therewith, the size and positions of said vanes forming together with said body a plurality of resonators and determining substantially a mean frequency to which the magnetron may be tuned, magnetic pole pieces xedly mounted inside said supporting body and positioned on opposite sides of said resonators, a guide ring concentrically mounted on one of said pole pieces, a plurality of guide rods journaled in said guide ring, `an L-ring and a C-ring iixedly mounted on said rods and having tuning portions positioned to enter into or egress from said resonators when said guide rods are moved longitudinally, and mechanical means coupled to said body for producing said longitudinal motion for tuning said magnetron over a given range, and means for greatly increasing said tuning range comprising a movable magnetic pole piece positioned on one side of said resonator to provide a variable flux path between itself and one of said mounted pole pieces, and means coupling said movable pole piece to said mechanical means.

6. The magnetron according to claim 5, wherein said movable pole piece is enclosed in a copper housing positioned to contact said envelope portion, whereby the heat in said pole piece is rapidly conducted therefrom.

7. The magnetron according to claim 5, wherein said movable pole piece is fastened at one end to said C-ring and at the opposite end to said mechanical means, whereby-said mechanical means moves unitarily the pole piece together with said L-C rings.

References Cited in the tile of this patent UNITED STATES PATENTS mmm l* 

